plate load test

[geoBrendan]

hello!

please in performing a plate load test, what is the most important parameter we look out for to report on?
How important is the modulus of subgrade reaction?
How much does the time taken for a particular test say about the test.
thank you in advance.

Brendan

 

[oldestguy]

More information on why a test is run and plate size would help.

 

[geoBrendan]

thank you oldestguy for your interest.

I am working with a plate size of 600 mm and the test is to determine the bearing pressure for thermal power plant.

 

[BigH]

The problem with plate load tests, in my humble view, for anything other than road pavement design is that they stress such a limited depth that, for a thermal power plant size foundations, would be, again, in my view, a joke. A 600 mm plate would be good for footings of, say, 1 to possibly 1.5 m wide.

Case history: In India, on the Calcutta clay plain, a structural engineer asked for a plate load test for a 10 m high retaining wall (RE wall). He got a very high strength - because the plate test was done is a 2 m old fill - he felt that something like 400 kPa would be a safe bearing pressure - hence he would build the wall without any ground treatment (that we had done at something like 20 other such locations in the general area). However, under this 2 to 3 m fill was 6 m of clay having an SPT value in the range of 1 to 3; under that was a clay with an SPT value in the order of 15 (reasonable). Had the retaining wall been constructed it would have undoubtedly failed. We dished the plate load test results and put in wick drains. Had 400 mm of settlement under a 4 m high stage load.

 

[Okiryu]

BigH, good case history. I am involved in a project where the specs calls for plate bearing tests, and noted also that if you do not have a good subgrade for the plate (the excavator made a large disturbance of the subgrade soils and the plate was installed just there) you can obtain unreliable results.
What size of plate do you use in India?

 

[Ron]

ALWAYS do at least a manual auger boring to 6-8 feet below the plate load test location before assessing the results!

BigH showed why!

 

[ATSE]

Do not use a plate load test for foundation design. The test will give you misleading information (artificially high stiffness). Okay for pavement design and lightly loaded slabs only.